Environmental laws and international standards for the quality of diesel and gasoline have set the sulfur content in diesel and gasoline to less than 50 ppm in most countries. Catalytic hydrodesulfurization is a widely used technology for desulfurization of gasolines in the refining industry.
FIG. 1 illustrates one embodiment of a one stage catalytic hydrodesulfurization process 5. The feed 10 is preheated in a heat exchanger 15 and mixed with hydrogen 20. The feed 10 and hydrogen 20 are introduced into reactor 25 where any dienes present are saturated. The effluent 30 is mixed with hydrogen 20 and sent to heater 35. The heated mixture 40 is mixed with hydrogen 20 and sent to the catalytic hydrodesulfurization reactor 45 where the sulfur content is reduced. The effluent 50 is sent to product separator 55 where the gas 60 is separated from the low sulfur liquid 65. The recovered hydrogen rich gas 60 is sent to a recycle gas scrubber 70 for hydrogen sulfide removal, and the cleaned hydrogen gas 20 is recycled back to the reactor. Hydrogen sulfide is removed in stream 75. The low sulfur liquid 65 is sent to a debutanizer 80 where the light ends 85 are separated from the low sulfur naphtha 90. Make-up hydrogen 22 can be added as needed.
FIG. 2 illustrates one embodiment of a two stage catalytic hydrodesulfurization process 105. The feed 110 is preheated in a heat exchanger 115 and mixed with hydrogen 120. The feed 110 and hydrogen 120 are introduced into reactor 125 where any dienes present are saturated. The effluent 130 is mixed with hydrogen 120 and sent to heater 135. The heated mixture 140 is sent to the first stage catalytic hydrodesulfurization reactor 145 where the sulfur content is reduced. The effluent 150 is sent to an interstage separator 155 where the gas 160 is separated from the low sulfur liquid 165. The hydrogen rich gas 160 is sent to a recycle gas scrubber 170 for hydrogen sulfide removal, and the cleaned hydrogen gas 120 is recycled back to the reactor. Hydrogen sulfide is removed in stream 175. The low sulfur liquid 165 is mixed with hydrogen 120 and sent to the second stage catalytic hydrodesulfurization reactor 180 where the sulfur content is further reduced. The effluent 185 from the second stage catalytic hydrodesulfurization reactor 180 is sent to product separator 190 where the gas 195 is separated from the low sulfur liquid 200. The gas 195 from the second stage is mixed with the gas 160 from the first stage catalytic hydrodesulfurization reactor 145 and sent to the recycle gas scrubber 170. The low sulfur liquid 200 is sent to a debutanizer 205 where the light ends 210 are separated from the low sulfur naphtha 215. Make-up hydrogen 122 can be added as needed.
For feeds with high sulfur content, reducing the sulfur content to less than 50 ppm requires high temperatures and pressures, which makes catalytic hydrodesulfurization process very expensive. In addition, the severe operating conditions result in the rapid loss of catalyst activity, particularly for oils with high sulfur content.
There is a need for a lower cost process for removing sulfur from naphtha.